The present invention relates generally to a magnetic disk inspection method and its system for inspecting a magnetic disk. The invention particularly relates to a magnetic disk inspection method and its system suitable for cassette-transfer, i.e., suitable to put magnetic disks in a cassette and load them to an inspection device and to put inspected magnetic disks in a cassette and take them out.
In a magnetic disk manufacturing line, a defect on the surface of an in-process magnetic disk is optically inspected. In this step, the magnetic disks put in a cassette are loaded into an inspection device, which takes out the magnetic disks one by one from the cassette and inspects them. The inspection device then returns the inspected magnetic disks to the cassette and transfers them to the next step.
As described above, magnetic disks are put in a cassette and taken in and out of an inspection device. In this respect, for example, JP-A-8-22619 (Patent Document 1) describes the fact that the inspection device takes out the magnetic disks one by one from the cassette for inspection, divides the inspected magnetic disks into non-defective products and defective products and stores them in corresponding separate cassettes.
The magnetic disk inspection device described in Patent Document 1 is configured as below. The magnetic disk inspection device takes out magnetic disks from a cassette and sequentially shifts the magnetic disks among a plurality of inspection means for performing a plurality of respective inspections. In addition, after a series of the inspections have been finished, the inspection device stores the magnetic disks in corresponding collection cassettes.
However, a plurality of inspection devices not necessarily can inspect a single magnetic disk at the same throughput. In some inspection step, the plurality of inspection devices may have to be used for inspections in accordance with a difference in throughput among the inspection devices.
Patent Document 1 does not consider the case where if a plurality of the same inspection devices are used for inspection as described above, a magnetic disk is loaded from a cassette to the inspection devices.